K-9 Mail app will become Thunderbird's Android email client

Martin Brinkmann
Jun 13, 2022
Updated • Jun 13, 2022

The developers of the open source Thunderbird email client confirmed today that the open source Android email app K-9 Mail will become Thunderbird for Android.

k-9 mail android

Thunderbird product and business development manager Ryan Lee Sipes confirmed in May 2022 that Thunderbird would become available for Android soon. The release would fill a gap, as Thunderbird has been available for desktop operating systems only up until now. The Android version enables Thunderbird users to sync data between desktop versions and their mobile Android devices.

The development of an Android email client from the ground up was one of the options that the team discussed, but it would have been a large project that would have required considerable effort and resources. The idea to collaborate with an existing open source email project for Android was born in 2018, when Sipes started talking to Christian Ketterer, the K-9 Mail project maintainer, about potential collaborations.

K-9 Mail "aligns perfectly with Thunderbird's values of using open standards, respecting the user, and enabling power users with unmatched customization" according to Sipes.  Ketterer has joined the Thunderbird team already, "bringing along his expertise and experience with mobile platforms", and the K-9 Mail application.

Thunderbird will "devote financial and development resources to improving K-9 Mail", including an improved account setup, something which Thunderbird received already in a recent update, improved folder management, support for message filters, and the option to sync data between desktop and mobile clients. The team expects to introduce synchronization support in the Summer of 2023.

K-9 Mail will turn into Thunderbird for Android eventually, but this won't happen overnight. The client will undergo visual changes to align it closely with Thunderbird.

K-9 Mail remains available, but users who have installed it will experience transformations in the coming months and years to align the email application closely with Thunderbird's brand and feature set.

The latest interface update has seen mixed reviews. Some users who use multiple email accounts in the application stated that they find it less intuitive to use. Others like its open source nature and that development is financed by donations.

Closing Words

Joining forces with an existing application and developer makes sense on lots of levels. K-9 Mail is already available and it will take less time to make it look and feel like Thunderbird. Creating an app from ground up would take more resources and more time, and users would probably be unhappy if the initial version would lack certain expected features.

The lead developer and team need to take user criticism seriously, as the 3.1 out of 5 stars rating is not the greatest. There is a good chance that several Many of theses will be addressed, thanks to additional development resources becoming available.

Now you: what is your take on the decision?

K-9 Mail app will become Thunderbird's Android email client
Article Name
K-9 Mail app will become Thunderbird's Android email client
The developers of the open source Thunderbird email client confirmed today that the open source Android email app K-9 Mail will become Thunderbird for Android.
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  1. Derek Clements said on June 15, 2022 at 4:57 am

    Hi Martin and fellow readers.
    Very interesting news and I’ll be watching the developments in the metaphorical sense at least. I will also be keen to digest further comment from you all.
    Stay well :)

  2. ShintoPlasm said on June 14, 2022 at 7:44 am

    For once a sensible approach from the open-source community – instead of forking/bickering, re-using something that works.

  3. owl said on June 14, 2022 at 1:18 am

    From the official announcement of the “Thunderbird” project (excerpted and quoted below)
    Revealed: Our Plans For Thunderbird On Android
    June 13, 2022
    Jason Evangelho

    Want to talk directly with the Thunderbird team about it? Join us for a Twitter Spaces chat (via @MozThunderbird) on Wednesday, June 15 at 10am PDT / 1pm EDT / 7pm CEST). I’ll be there alongside cketti and Ryan to answer your questions, and discuss the future of Thunderbird on mobile devices.
    @MozThunderbird: twitter.com/mozthunderbird

    Frequently Asked Questions: Thunderbird Mobile and K-9 Mail
    We’ve published a separate FAQ, addressing many of the community’s questions and concerns. Check back there from time to time, as we plan to update the FAQ as this collaboration progresses.

  4. some1 said on June 13, 2022 at 11:31 pm

    FairEmail is great on Android. why reinvent the wheel?!

    1. 2wq4Y36 said on June 15, 2022 at 2:38 am

      k9 predates fairmail, so by your logic fairemail shouldn’t exist.

      1. some1 said on June 15, 2022 at 11:10 am

        Yes, but K9 was very buggy and terrible.

  5. Anonymous said on June 13, 2022 at 11:26 pm

    Will this be good as Aqua Mail Pro?

  6. clake said on June 13, 2022 at 9:10 pm

    I have been using k9 for years. Recently, though, a couple accounts had to be deleted due to their switch to Oauth2. The additon of Oauth will help, but I hope it is not dependent on google play services as I usually disable that.

    Fair Mail works fine for the time being with ymail account/Oauth2 and google play services disabled – only needed to disable some notifications.

  7. svim said on June 13, 2022 at 8:53 pm

    Well this is really interesting and I’m looking forward to this merger. I stopped using the K-9 Mail app just this year after several years (over a decade) and three phones but after reading this article will probably switch back when the dust settles.
    K9 Mail has a nice, clean, basic user interface and a really extensive, feature-rich number of options in its Settings menu.
    Thanks for posting this article.

  8. Iron Heart said on June 13, 2022 at 8:17 pm

    Thunderbird already saying bye bye to Gecko as they know it is untenable… K-9 Mail is not Gecko-based. That also means no Thunderbird extensions will run there.

    1. Yash said on June 14, 2022 at 7:18 am

      Was there any popular or big or open source email client on Android Gecko based in the first place?

    2. m3city said on June 13, 2022 at 10:59 pm

      Any source for that?

      1. Iron Heart said on June 14, 2022 at 9:10 am


        Take a look at K-9 Mail‘s open source code, that is not Gecko. They also didn‘t say anything about porting K-9 Mail to the Gecko engine…

      2. m3city said on June 14, 2022 at 2:59 pm

        @Iron Heart

        That says nothing in regard to yours “Thunderbird already saying bye bye to Gecko as they know it is untenable”. You got me intrigued by that statement, however it came out as usual.

  9. Yash said on June 13, 2022 at 7:59 pm

    Wonderful news. Although Fairemail collab would’ve been great too, more of a cheat code to improve privacy, K-9 mail is pretty damn good as well.

  10. David said on June 13, 2022 at 7:50 pm

    Good news. As an iOS user I hope they make a similarly inspired choice.

  11. foolishgrunt said on June 13, 2022 at 6:23 pm

    Sounds like a good deal to me?

    I currently use Fairmail on Android, but would certainly be open to considering a switch.

  12. motang said on June 13, 2022 at 4:52 pm

    Good news, I was wondering why making another open source client when we have an excellent one (K9-Mail) for Android. You would be competition with a niche market. But glad that’s not what’s happening, but a merger my favorite Android mail client to Desktop mail client.

  13. Artem S. Tashkinov said on June 13, 2022 at 4:05 pm

    This is actually exciting news!

    K-9 Mail has a ton of long standing issues and missing features which require an additional manpower the Thunderbird project could provide.

    The most pressing one of course, is missing OAuth support.

    1. Hitomi said on June 13, 2022 at 7:49 pm

      Are we talking OAuth2?

      Personally I always considered this protocol always to be ugly crutches. So we moved from low entropy passwords to high entropy tokes and instead of manually copy pasting them into our clients we hide it behind tons of code to make it accessible to normies.

      The only thing it solves is keeping it easy for the tech illiterates. Now FIDO2, that is a real solution. Nothing will ever beat good old challenge–response authentication in terms of raw security.

    2. Martin Brinkmann said on June 13, 2022 at 6:56 pm

      Missing OAuth support is already ready, a new version is just waiting for Google’s approval according to the lead developer.

      1. NeonRobot said on June 14, 2022 at 7:50 am

        Looks like a good time to stop updating k-9.

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